KR20000062355A - Method for Producing Olefins, in Particular Propylenes, by Dehydrogenation - Google Patents

Abstract

The present invention relates to the corresponding paraffinic hydrocarbons in the periodic table of group IVB elements (eg TiO ₂ or ZrO ₂ ) and possibly one or more Group VIIIB elements (eg palladium, platinum or rhodium) and / or group VIB. Compounds of transition metals of elements (eg chromium, molybdenum or tungsten) and / or oxides of rhenium and / or tin, as well as compounds of alkali or alkaline earth metals, groups IIIA or IIIB, or zinc Dehydrogenation on contained catalysts relates to the production of propylene, in particular from other olefinically unsaturated hydrocarbons, or propane.

Description

Process for producing olefins, especially propylene by dehydrogenation {Method for Producing Olefins, in Particular Propylenes, by Dehydrogenation}

Currently propylene is mostly separated from the product mixture formed in the vapor cracking of light naphtha. It is desirable to have more suitable raw material components for economic and other reasons. Another method of separating propylene from the mixture is dehydrogenation of propane.

As a non-oxidative route, propylene can be obtained by dehydrogenation of propane using a noble metal catalyst such as Pt / Al ₂ O ₃ , Pt / Sn / Al ₂ O ₃ or a catalyst free of precious metal such as Cr / Al ₂ O _3. have. This reaction is very exothermic and proceeds at a satisfactory rate only at high temperatures. This decomposes propane to produce ethylene and methane and at the same time enhances the secondary reaction of hydrogenating ethylene with hydrogen generated in dehydrogenation. The selectivity of the reaction decreases significantly with increasing conversion due to byproduct-dependent competitive reactions, doubting the industrial viability of the reaction. In addition, secondary reactions result in carbon deposits on the catalyst used and must be regenerated after a relatively short period of time.

In industrially achieved methods, dehydrogenation is carried out at low pressures and relatively high temperatures and the catalyst is continuously regenerated using atmospheric oxygen [Energy Prog. (1986), 6 (3) 171-6 and Chem. Eng. Today, Copying Uncertainty, Aust. Chem. Eng. Conf. 11th (1983), 663-71. This method can be carried out using a Pt / Al ₂ O ₃ catalyst in a mobile phase at 600-700 ° C. and a pressure of 2-5 bar.

The process described in WO 9523123 uses a Cr / Al ₂ O ₃ catalyst which functions periodically, i.e. requires a regeneration process. In this method, propane is preheated using waste heat generated from the combustion of carbon. Pt / Sn / Al ₂ O ₃ catalysts are known from Shiyou Huagong (1992), 21 (8), 511-515. This reference also describes that such catalysts may be doped with potassium or magnesium. Doping with tin lowers deactivation despite the formation of carbon deposits [Stud. Surf. Sci. Catal. 1994, 88, 519-24.

An oxidative catalyst comprising a redox-active element that does not exist in the lowest oxidation state is described in EP-A-403 462.

Dehydrogenation of propane with zeolites of the ZSM-5 type is also known. Doping such zeolite with zinc affects the acid-base behavior of the zeolite, i.e., the cracking reaction is greatly suppressed [J. Chin. Inst. Chem. Eng. (1990), 21 (3), 167-72.

Known methods have the disadvantage that the selectivity decreases significantly, especially as the conversion rate increases. In addition, the frequent regeneration of the catalyst is very disadvantageous as an industrial method.

It is an object of the present invention to eliminate the aforementioned drawbacks and to dehydrogenate the corresponding paraffinic hydrocarbons to enable the production of propylene and other low molecular weight olefins and to provide a catalyst which achieves high selectivity even at high conversions.

The inventors have found that this object is achieved using a ceramic oxide based catalyst of group IVB of the periodic table, which may comprise a dehydrogenating active element and possibly further elements.

Suitable ceramic oxides are in particular zirconium oxide (ZrO ₂ ) and titanium oxide (TiO ₂ ). The ceramic oxide may be doped with Group VIB and Group VIIIB metals. Suitable dehydrogenation-active elements are particularly suitable for Group VIIIB metals, platinum and palladium which are precious metals, with platinum being preferred.

If a noble metal is used as the dehydrogenation-active element, it is possible to add metals which can slow down the sintering rate of the noble metal, for example Re, Ir and Sn, in particular Re and Sn.

Additional elements are known which can affect the acidity of the catalyst surface or stabilize the precious metal against sintering. These additional elements are both IA and IIA elements, ie Li, Na, K, Rb, Cs and Mg, Ca, Sr and Ba. Suitable elements of group IIIB are, in particular, Y and La and also rare earth elements. Zinc has also been found to be effective.

While the use of group IVB ceramic oxides is essential for the purposes of the present invention, other components are also important for the base reaction and play a supporting role. Thus, other dehydrogenation-active metals, for example group VIB, in particular chromium or molybdenum, may be present in place of the precious metals.

It is important in the present invention that the crystalline phase of zirconium oxide is stable under the conditions of dehydrogenation. If square ZrO ₂ is used, it can be stabilized by doping with La or Y.

Compared with known catalysts, the catalysts of the invention have the advantage of higher selectivity and at the same time higher conversion in the dehydrogenation of propane to propylene. It has also been found to further benefit that the catalyst of the present invention can function without the additional hydrogen that must be used to inhibit the production of carbon deposits. Further advantages are large mechanical strength, long operating life and easy molding.

To prepare the catalyst of the invention, it is possible to use amphoteric oxides of zirconium and titanium or mixtures thereof or suitable precursors which can be converted to oxides by firing.

This method of preparation may be selected from known model methods, for example sol-gel methods, precipitation of salts, dehydration of the corresponding acid, dry mixing, slurding or spray drying.

Doping with the basic compound can be carried out during preparation, for example by coprecipitation or by impregnation of ceramic amphoteric oxide with a suitable alkali metal or alkaline earth metal compound or the like continuously.

The dehydrogenation-active component is generally applied by impregnation with a suitable compound of the relevant element. These compounds are chosen such that they can be converted to the corresponding metal oxides by firing. However, the dehydrogenation-active component may also be applied by other methods such as spraying instead of impregnation. Suitable metal salts are, for example, nitrates, acetates and chlorides of the corresponding metals, and anionic complexes of the metals used are also possible. Preference is given to using H ₂ PtCl ₆ or Pt (NO ₃ ) _{2 of} platinum and Cr (NO ₃ ) ₃ or (NH ₄ ) ₂ CrO ₄ of chromium. When a noble metal is used as the dehydrogenation-active component, suitable precursors include one of the known methods, for example a corresponding precious metal sol which can be prepared by reducing the metal salt with a reducing agent in the presence of a stabilizer such as PVP. The preparation method is described in detail in DE 195 00 366.

The catalyst can be used in the form of a fixed bed or for example a fluidized bed and has a suitable form. Suitable forms are, for example, granules, pellets, monoliths, spheres or extrudates having a suitable cross section (eg wagon wheels, features, rings).

The content of alkali metals, alkaline earth metals, IIIA or IIIB metals, rare earth metals or zinc is 20% by weight, preferably 1 to 15% by weight, particularly preferably 1 to 10% by weight or less. Alkali and alkaline earth metal precursors used are advantageously compounds which can be converted directly to the corresponding oxides by firing. Suitable examples are hydroxides, carbonates, oxalates, acetates or mixed hydroxycarbonates.

If the ceramic support is additionally or exclusively doped with IIIA or IIIB metals, the starting compound in this case should also be one that can be converted to the corresponding oxide by firing. If lanthanum is used, examples of suitable compounds are lanthanum oxide carbonate, La (OH) ₃ La ₃ (CO ₃ ) ₂ , La (NO ₃ ) ₃ or lanthanum compounds containing organic anions, for example lanthanum Acetate, lanthanum formate or lanthanum oxalate.

The content of dehydrogenation-active component in the catalyst is up to 10% by weight. It is also possible to use catalysts which do not contain dehydrogenation-active elements. When the catalyst is doped with a dehydrogenation-active element of group VIIIB as the dehydrogenation-active element, its content is from 0 to 10% by weight, preferably from 0.2 to 8% by weight, particularly preferably from 0.5 to 2% by weight. to be. When the catalyst is doped with noble metal as the dehydrogenation-active component, the content is from 0 to 5% by weight, preferably from 0.2 to 2% by weight, particularly preferably from 0.5 to 1.5% by weight.

The catalyst has a BET surface area of 500 m 2 / g, preferably 10-300 m 2 / g, particularly preferably 20-100 m 2 / g or less. The pore volume is generally 0.1 to 1 ml / g, preferably 0.15 to 0.6 ml / g, particularly preferably 0.2 to 0.4 ml / g. The average pore diameter that can be measured by Hg permeation analysis is 0.008 to 0.06 μm, preferably 0.01 to 0.04 μm.

The dehydrogenation of propane is carried out at 300-800 ° C., preferably at 450-700 ° C., and at a pressure of 10 mbar to 100 bar, preferably at 100 mbar to 40 bar, with a weight hourly space of 0.01 to 100, preferably 0.1 to 20 At a rate hourly space velocity (WHSV) ([starting material g) · (catalyst g) ⁻¹ · h ⁻¹ ]), in addition to dehydrogenated hydrocarbons, diluents such as CO ₂ , N ₂ , inert gases or vapors. If necessary, that is, hydrogen can be added to the hydrocarbon stream under stringent reaction conditions, and the ratio of hydrogen to the hydrocarbon stream can be 0.1 to 100, preferably 1 to 20. The added hydrogen is a catalyst. It acts to remove the carbon deposits formed on the surface.

In addition to the continuous addition of gases to prevent carbon deposits during the reaction, it is sometimes possible to regenerate the catalyst through hydrogen or air. The regeneration itself is carried out at 300-900 ° C., preferably at 400-800 ° C., using a free oxidant, preferably air, or preferably in a reducing atmosphere, preferably with hydrogen. Regeneration may be performed at pressures below atmospheric pressure, atmospheric pressure or above atmospheric pressure. Preferred is a pressure of 500 mbar to 100 bar.

Catalyst manufacturing

<Examples 1 to 4>

4, the M NH ₃ solution was added to a solution of water, 50 ml of ZrOCl ₂ and H ₂ O 24.85 g and La (NO _{3) 3} 6H ₂ O 1.33 g and stirred until precipitation is no longer observed. The precipitate was filtered off, washed with water until free of chloride and stirred at 120 ° C. for 16 h. The dried precipitate was suspended in 50 ml of 0.02 M (NH ₄ ) ₂ CrO ₄ solution and the supernatant was evaporated at 50 ° C. The residue was dried at 120 ° C. for 16 hours and calcined at 600 ° C. for 4 hours. The finished catalyst contained 0.66% chromium and 5.3% lanthanum. The crystalline phase of zirconium dioxide was found to be mostly square by X-ray analysis. The primary particle diameter of zirconium dioxide was measured at about 5 nm by TEM.

In Example 1, a membrane prepared catalyst was used. In Example 2, the same catalyst was used after regeneration at 500 DEG C using oxygen in the atmosphere. The catalyst regenerated twice using oxygen in the atmosphere was used in Example 3, and the catalyst regenerated three times was used in Example 4.

<Examples 5 and 6>

The catalyst was prepared by impregnating ZrO ₂ (support SN 9316335, Norton, 46 m 2 / g, mostly monoclinic) with Pt (NO ₃ ) ₂ and Sn (OAc) ₂ . The Pt content was 1% by weight and the Sn content was 0.5% by weight. The catalyst was calcined at 650 ° C. for 3 hours.

<Example 7>

The catalyst was mostly impregnated with monoclinic ZrO ₂ (support SN 9316335, Norton, 49 m 2 / g) with a solution of 0.821 g of Cr (NO ₃ ) ₃ .9H ₂ O in 2.5 ml of water followed by La (NO) in 2.5 ml of water. ₃ ) ₃ was prepared by impregnation with 1.763 g of a solution. The catalyst was dried at 120 ° C. for 16 hours and calcined at 500 ° C. for 2 hours. The finished catalyst had a chromium content of 0.9 wt% and a lanthanum content of 4.5 wt%.

<Comparative Examples C1 to C4>

Comparative catalysts (C1: 10% Cr / Al ₂ O ₃ , C2: 1% Cr / Al ₂ O ₃ and C3: 5% Cr / Al ₂ O ₃ ) were compared with α-Al ₂ O ₃ (9.5 m 2 / g) Prepared by impregnation with different amounts of Cr (NO ₃ ) ₃ . This catalyst was dried at 120 ° C. for 6 hours and then calcined at 500 ° C. for 2 hours. Comparative catalyst C4 was prepared by impregnating the same Al ₂ O ₃ support with Pt (NO ₃ ) ₂ . The catalyst was dried at 120 ° C. for 16 hours and then calcined at 500 ° C. for 2 hours.

Dehydrogenation

Dehydrogenation was carried out in a micro- stationary pulse reactor at 500 ° C. To this end, about 0.6 g of catalyst was weighed into the micro-fixed phase and propane gas was passed through the pulses at atmospheric pressure, ie regularly interrupted flow, without hydrogenation. The reaction product was quantitatively analyzed by on-line GC in each pulse. Helium carrier gas was flowed through the reactor between each pair of successive propane pulses (about 1.5 minute intervals).

One pulse consisted of about 100 μl of propane. The flow rate of the carrier gas was about 21.5 ml / min. The residence time, depending on the bed height (10-25 mm) of the catalyst, was about 1 to 2 seconds. WHSV through the catalyst during the pulse, also dependent on bed height, was 1.7 to 3.4. The results obtained are shown in Table 1 and are based on the maximum conversion achieved.

Performance of Catalysts in Dehydrogenation of Propane in Pulsed Reactors Example catalyst Residence time [s] Floor height Y [%] Conversion rate [%] Selectivity [%] One La / Cr / ZrO ₂ 0.8 15 mm 50 54 92 2 La / Cr / ZrO ₂ 0.8 15 mm 49 52 92 3 La / Cr / ZrO ₂ 0.8 15 mm 47 51 92 4 La / Cr / ZrO ₂ 0.8 15 mm 49 53 92 5 1% Pt / 0.5% Sn / ZrO ₂ 1.2 23 mm 49 53 92 6 1% Pt / 0.5% Sn / ZrO ₂ 1.2 23 mm 43 44 97 7 La / Cr / ZrO ₂ 1.3 24 mm 35 36 96 C1 10% Cr / Al ₂ O ₃ 1.3 25 mm 25 26 96 C2 1% Cr / Al ₂ O ₃ 1.3 24 mm 14 18 79 C3 5% Cr / Al ₂ O ₃ 1.2 23 mm 22 23 95 C4 1% Pt / Al ₂ O ₃ 1.3 24 mm 5 59 9

It should be noted that due to the shorter residence time and the interval of about 1.5 minutes between the pulses, a significantly higher conversion is achieved compared to the equilibrium position (500 ° C.) by the pulse process where no thermodynamic equilibrium is established. However, this method allows a good comparison of selectivity at high conversion rates.

The catalyst of the present invention showed higher conversion than the comparative catalyst achieved at relatively high selectivity at the same temperature. Thus, the catalysts of the present invention exhibited significantly higher yields than the comparative catalysts.

Claims (15)

A process for the preparation of olefins having 2 to 5 carbon atoms in the longest chain by dehydrogenation of the corresponding paraffinic hydrocarbons on a catalyst, characterized in that the catalyst used comprises oxides of group IVB elements of the periodic table. The method of claim 1, wherein the catalyst used further comprises at least one element selected from Group VIIIB elements, Group VIB elements, ruthenium, tin, compounds of alkali metals or alkaline earth metals, compounds of Group IIIA or Group IIIB and / or zinc. Method comprising a. 3. Process according to claim 1 or 2, characterized in that propylene is obtained from propane. A catalyst for dehydrogenating a corresponding saturated hydrocarbon to produce other olefinically unsaturated hydrocarbons, or in particular propylene from propane, characterized in that it comprises an oxide of a group IVB element of the periodic table. The method of claim 4, further comprising at least one element selected from Group VIIIB elements, Group VIB elements, ruthenium, tin, compounds of alkali or alkaline earth metals, compounds of Group IIIA or Group IIIB and / or zinc. Catalyst. The catalyst according to claim 4 or 5, characterized in that the crystal modification of the transition metal oxide comprises more than 90% homogeneous phase. The catalyst according to claim 4 or 5, comprising zirconium oxide. 8. The catalyst of claim 7 comprising zirconium oxide in a square modification. The catalyst according to claim 4 or 5, comprising titanium oxide. The catalyst according to claim 4 or 5, comprising 0.005 to 5% by weight of palladium, platinum, rhodium and / or rhenium. The catalyst according to claim 4 or 5, comprising sodium or potassium as the alkali metal. The catalyst according to claim 4 or 5, comprising a lanthanum, yttrium, gallium, indium or thallium compound as the compound of Group IIIA or IIIB. The catalyst according to claim 4 or 5, comprising chromium and / or tungsten compounds as group VIB compounds. The catalyst according to any one of claims 1 to 13, having a BET surface area of from 10 to 500 m 2 / g. The method according to any one of claims 1 to 14, wherein at least 10% of the pores have a width of more than 20 nm and have pores having a width of 2 to 60 nm having a specific pore volume of 0.1 to 1 ml / g. A catalyst, characterized in that.